The present invention is generally related to the collection of gas from subterranean formations, and more particularly is directed to a method for collecting gas from subterranean formations having a plurality of spaced-apart seams containing the gas.
Coal seams are commonly found in a spaced-apart relationship in subterranean formations and generally contain therein a significant amount of methane gas which escapes therefrom as the coal is mined.
In conventional coal mining, the released methane gas must be vented in order to provide a safe working environment for workers employed in the mining operation.
The methane gas is hazardous from a health stand-point, as it is poisonous, and also from a safety stand-point, as it forms combustible mixtures with oxygen.
Although a considerable amount of effort has been put forth to ventilate coal mines to remove methane gas, such as air dilution systems within the mine and the drilling of holes within the coal seams in advance of mining to draw off the methane, little has been done on a commercial basis to extract and collect gases, such as methane, from underground seams without the subsequent mining of the seams to remove coal.
Co-pending U.S. applications, entitled, "Multiple Level Methane Drainage Shaft Method," Ser. No. 420,149, filed on Sept. 20, 1982, now U.S. Pat. No. 4,452,489 and "Multiple Level Methane Drainage Method," Ser. No. 609,473, filed on May 11, 1984 disclose a method for the recovery of methane gas from underground, or subterranean formations, irrespective of later mining of the seams for the coal content.
These methods are important in that they are suitable for collecting methane gas from coal seams in which the thickness of the coal seams is significantly less than that needed for economic commercial mining of the coal from the coal seams.
These methods, however, require extensive underground excavation in order to establish a methane gas collection system within a plurality of spaced-apart coal seams.
Needless to say, such excavation is expensive and time-consuming. The present method and apparatus is directed to the recovery of gas from underground formations having a plurality of spaced-apart seams containing gas. However, little excavation is necessary beyond that of the sinking of a generally vertical shaft from the earth's surface and intersecting a plurality of these seams.
The apparatus of the present invention enables the drilling of a plurality of horizontal holes in a plurality of the subterranean spaced-apart seams and the collection of gas therefrom.
In addition, the thickness of the seam is not a limitation to the utilization of the method and apparatus of the present invention.